Neodymium-YAG lasers with laser beam guides and focusing optics are used for operations on the human eye. Since in the case of such operations, the so-called optical opening is larger than the laser beam spot, hitherto no attention has been paid to the variation in the spot size and consequently also to the associated variation in the angle of the marginal beams of the focused beam, i.e. the variation of the so-called divergence angle. Thus, known neodymium-YAG lasers are constructed in such a way that the laser beam is focused with a given fixed divergence angle.